Effects of Severe Freezing Periods and Discharge on the Formation of Ice Jams at Salmon, Idaho
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
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Large ice jams on the Salmon River have reached Salmon, Idaho, and resulted in major flood damage during 16 winters since the winter of 1936-37. Two recent ice jams, in February 1982 and January 1984, caused flooding that resulted in damages of 1 million and 1.8 million respectively. A detailed analysis of the winter air temperature records from 1936-37 through 1991-92 revealed a strong relationship between the duration and intensity of severe cold periods, the air temperature record prior to the severe cold periods, and the occurrence of ice jams reaching the city of Salmon that result in flooding. A threshold condition is identified from which the probability of icejams reaching the city can be determined from inspection of forecasted air temperatures. It was found that once an icejam reaches the city, average daily air temperatures of approximately 18 deg F are necessary to keep the jam in place. The effects of discharge on ice thickness, and therefore ice jam length, are shown to be minor and no relation could be found in this study. An ice control structure located upstream of the city of Salmon appears to be helping to alleviate ice-jam flooding. Air temperatures, Flooding, Ice boom, Ice jams, Flood control, Freezing degree-days, Ice control, Salmon River.
- Environmental Health and Safety